1. Field of the Invention
The present invention relates to an apparatus for executing overedge stitch seams in trimming sewing machines, of the type comprising: at least one needle carrying a respective sewing thread and reciprocated with a rectilinear motion through a workpiece moving according to a given sewing direction; a lower looper carrying a respective interlacing thread, which looper operates under the workpiece and performs a reciprocating motion in a direction transverse to the sewing direction so that it cyclically engages through a loop formed by the sewing thread inserted through the workpiece; an upper looper reciprocated according to a curved trajectory extending on either side of the lateral edge of the workpiece, to engage the interlacing thread and arrange it over the workpiece so that it is interlooped by the sewing needle moving towards the workpiece.
It is also an object of the present invention to provide a method put into effect by said apparatus, said method comprising the steps of: inserting a sewing thread folded over into two side by side portions, through the workpiece; engaging an interlacing thread folded over into two consecutive and side by side portions, in a loop defined by the portions of the sewing thread inserted through the workpiece; carrying one of the interlacing thread portions astride a lateral edge of the workpiece; interlooping the sewing thread into the space defined between the interlacing thread portion over the workpiece and the workpiece edge, simultaneously with a new insertion step of the sewing thread through the workpiece.
It is a further object of the present invention provides a new seam formed by the apparatus and method in question, said seam being of the type comprising: at least one sewing thread engaged through a workpiece according to insertion points aligned in a sewing direction parallel to a lateral edge of the workpiece itself; an interlacing thread interlooped with the sewing thread.
2. Prior Art
It is known that in the field of making garments or the like, the sewing operations for assembling the different garment parts and/or for achieving an aesthetic finish of the edges of the obtained article are often carried out with the aid of trimming sewing machines adapted to execute an overedge stitch seam along the edges of the mutually superposed workpieces that are automatically trimmed while the seam is being made.
For the formation of an overedge stitch seam one or more threads are required. More particularly, provision is made for at least one sewing thread associated with a needle driven with a reciprocating motion, generally in a vertical plane, through the workpiece that, by feed means operating in synchronism with other component parts of the sewing machine, is moved forward along a needle plate according to a given sewing direction. Upon the action of the needle, the sewing thread is inserted through the fabric and, when the needle starts its upward stroke, it forms a loop inside which an interlacing thread is normally inserted, which thread is engaged with the end of a lower looper located under the needle plate and provided with a reciprocating motion in a direction transverse to the sewing direction.
When the lower looper, and therefore the interlacing thread, have been conveniently engaged into the loop formed by the sewing thread, the interlacing thread is engaged by an upper looper provided with a reciprocating motion according to a trajectory extending on either side of the lateral edge of the workpiece. More particularly, the upper looper engages the interlacing thread so as to drag it along over the workpiece and prepare it for being interlooped by the needle and subsequently the sewing thread, when a new downward stroke is performed by the needle, following which the sewing thread will be inserted again through the workpiece in order to give rise to the formation of a new sewing stitch.
In a seam thus executed, the sewing thread is disposed on the "right side" of the workpiece, that is on that part which can be seen by an operator while the seam is being made, according to a plurality of rectilinear short lengths or portions parallel to the lateral edge of the workpiece, joined one after the other at the points where the needle has entered the workpiece. The interlacing thread, on the workpiece, is disposed so as to form a series of short lengths extending according to an oblique alternate course between each of the points where the needle insertion has occurred and the lateral edge of the workpiece. On the reverse side of the workpiece, that is the side facing the needle plate while a seam is being formed, the sewing thread is disposed so as to form, in the same manner as previously said with reference of the interlacing thread on the right side of the workpiece, a plurality of short lengths following each other according to an oblique alternate course between the insertion points of the needle an the lateral edge of the workpiece where the same portions of the sewing thread are engaged with the interlacing thread.
The overedge stitch seam of the above type listed under Nos. 502 and 503 in the Federal Standard Catalogue, as well as other types of overedge stitch seams, are sometimes also utilized as an ornamental finish along the edges of garments or the like.
The foregoing being stated, it is to be noted that in recent times there has been a great demand on the market for garments finished along their edges by seams executed with a particular type of stitch which in the art is usually referred to as "saddle stitch".
Presently these seams are executed by sewing machines comprising a needle carrying a sewing thread and reciprocated through the workpiece. Cooperating with the needle is a particular looper exhibiting a configuration similar to that of a common knitting machine needle provided with a closure latch, reciprocated according to a U-shaped trajectory extending astride the workpiece edge. Such a looper at each lowering step of the reciprocating movement, picks up the sewing thread and disposes it so that it can be interlooped by the needle under the workpiece and, at each raising step, picks up the sewing thread carried by the needle under the workpiece and moves it into readiness for being interlooped by the needle during the new downward stroke of the latter.
In conclusion there is the formation of a sewing chain with a single thread which lays on the right side of the workpiece according to a plurality of short lengths oriented perpendicularly to the lateral edge. On the reverse side of the workpiece, the sewing thread forms a plurality of consecutive short lengths disposed obliquely with an alternate course in the space existing between the points of the needle insertion and the lateral edge of the workpiece.
While finishing seams of the above type have been greatly appreciated on the market, it is pointed out that garment manufacturers encounter many problems in this type of working, first of all because it is necessary to set up a sewing machine expressly produced for the execution of said seams and in addition because said seams are used only on a limited typology of articles of clothing and consequently they could be no longer utilized should these articles be no longer required.
It is also to be noted that due to the structural conception of the looper and the particular movements it must perform, there are many restrictions in the operating speed of the sewing machines adapted to execute seams of the above specified type.